In the Release (R) 8/9 of a Long Term Evolution (LTE) system and the R10 of an LTE-Advanced system, a downlink control signaling is generally configured to be sent on the first N Orthogonal Frequency Division Multiplexing (OFDM) symbols of one Subframe (with reference to a definition with regard to the Subframe in the 3rd Generation Partnership Project (3GPP) TS 36.211), and those N symbols are generally called as a control signaling transmission area of a subframe. Here, in order to distinguish from a control signaling transmission area newly added in the new release, the control signaling transmission area of the R8/9/10 is called as a first control signaling transmission area in the present document.
The available transmission resources of the first control signaling transmission area are divided into multiple Control Channel Element (CCE) resource units, the resources occupied by the control information are allocated with CCE being a unit, a resource unit CCE here also can be further subdivided into multiple Resource Element Groups (REGs), a CCE consists of multiple discontinuous REGs, and normally 9 REGs constitute a CCE, and each REG is further composed of multiple basic resource units.
It can be seen that the control signaling transmission resources allocated by users are discontinuous, this brings a lot of difficulties in implementing the closed-loop precoding technology in a multi-antenna system, which causes that only the diversity technology can be used and the closed-loop precoding technology is difficult to be used in the control signaling area. The main reason is that, when the closed-loop precoding technology is used in the first control signaling transmission area, there exists a great design difficulty in the aspect of demodulation pilots and channel state information feedback, thus all control signalings in the existing releases only support the discontinuous resource transmission and the diversity technology.
In the releases after the R10, in order to enhance the transmission capacity of control channels and support the control signalings of more users, it is to consider to open up new control channel areas, and control signaling transmission resources of the same User Equipment (UE) can be continuous time-frequency resources so as to support the closed-loop precoding technology, thereby enhancing the transmission performance of control information.
Control signaling areas of the new releases (i.e., the releases after the Release 10 (called as the R10 for short)) and the old releases (i.e., the Release 8/9/10) is as shown in FIG. 1.
In this method, in a Physical Downlink Shared Channel (PDSCH) transmission area of the original R8/9/10, part of transmission resources are set apart to serve as a second control signaling transmission area, such that the closed-loop precoding technology can be supported when the control signallings are transmitted, thereby enhancing the control signalling capacity and supporting transmission of the control signallings of more users.
Here, in the second control signaling transmission area, a dedicated Demodulation Reference Signal (DMRS) in the R10 can be reused to demodulate the control signalings, which supports the precoding technology well. Due to the appearance of the second control signaling transmission area, the DMRS not only needs to support data demodulation, but also needs to support demodulation of the second category of control signalings transmitted within the first control signaling transmission area, and a new research subject is how to achieve the optimal downlink transmission under this condition.
FIG. 2 is a schematic diagram of distribution of the second category of control signalings and data information transmitted within a transmission resource block. The distributed situation of the second category of control signalings and data information shown in FIG. 2 can be further represented as shown in FIG. 3.
In order to waste no resources and avoid scheduling restrictions, situations where the data information and the second category of downlink control signalings are transmitted in an identical Resource Block (RB) shown in FIG. 2 and FIG. 3 will appear frequently. Only one situation is listed in this example, and of course, other situations are also included in practice.
Scheme 1: the second category of control signalings is demodulated by using DMRSs on the 6th OFDM symbol and the 7th OFDM symbol in FIG. 3, and the data information is demodulated by using DMRSs on the 13th OFDM symbol and the 14th OFDM symbol in FIG. 3.
The scheme 1 is actually equivalent to that the second category of control signalings and the data information are demodulated by using half of the DMRSs respectively, the demodulation performance will be reduced, and the channel estimation has no time-domain interpolation. Secondly, due to the truncation of DMRS, the transmission of data information of the second Slot (referring to a definition for the Slot in the 3GPP TS36.211) cannot support the transmission of layer 5, layer 6, layer 7 and layer 8 anymore, which loses the transmission ability of supporting 8 layers at most of the Multiple Input and Multiple Output (MIMO) when there are 8 antennas, but can only support 4 layers.
Scheme 2: the second category of control signalings is demodulated by using DMRSs on the 6th OFDM symbol, the 7th OFDM symbol, the 13th OFDM symbol and the 14th OFDM symbol in FIG. 3, the data information is also modulated by using the DMRSs on the 6th OFDM symbol, the 7th OFDM symbol, the 13th OFDM symbol and the 14th OFDM symbol in FIG. 3, but it is limited to using the identical DMRS port. Therefore, normal demodulation can be performed without truncating when using the existing DMRSs. However, since the identical DMRS port is used, the method brings certain limitations. For example,
the data and the control signalings are required to use the same transmission layer number and transmission power; or
the data information and the second category of control signalings are required to belong to an identical user.
The defects of the scheme 2 are that, the control signalings are appropriate for being transmitted in less layers, the data may be appropriate for being transmitted in more layers, the same number of layers brings the limitations. The robustness of control signalings is different from the transmission robustness requirements of data information, thus transmission powers may also be different, and the limitation of same power may also bring other problems. In addition, both the data information and the second category of control signaling information are required to belong to an identical user, which will have limitations on the scheduling in practice, go against the flexibility of scheduling, and have a certain extent of loss of scheduling gain.